The present invention relates to a semiconductor memory. More particularly, the present invention pertains to a technique which may effectively be utilized for, for example, a static type RAM (Random-Access Memory) which is employed as an arithmetic memory in an image processing system.
There is one type of image processing system which consists essentially of a CRT (Cathode-Ray Tube) display, a frame buffer memory and a bit map processor. This type of image processing system may incorporate an arithmetic memory for temporarily storing image data which is being prepared or changed. This arithmetic memory may be formed using, for example, static type RAMs such as those described in "Hitachi IC Memory Data Book", Hitachi, Ltd., Sept. 1983, pp. 243 to 247.
Conventional semiconductor memories, including these static type RAMs, are arranged such that one or more memory cells which are in a fixed positional relation to a given address signal are brought into a selected state, and data stored therein is then read.
In the image processing system of the type described above, a relatively important problem lies in zooming (reduction/enlargement) of the image being displayed. FIGS. 6a/6b and 7a/7b show one of the already-proposed arithmetic processing methods for effecting the above-described zooming process.
More specifically, in the case of FIG. 6a/6b a reduced image 6b reduced to, for example, 1/Z is to be obtained on the basis of image data concerning the displayed image 6a which has already been stored in the arithmetic memory. When an address (Xa.multidot.Ya) at which is disposed any picture element (va), in the reduced image 6b, is enlarged by substantially z times and projected on the original displayed image 6a, the pitch of the address (Xa'.multidot.Ya') is not always coincident with the pitch of the picture elements in the original displayed image 6a. For this reason, a value which is written as data concerning a picture element at the address (Xa.multidot.Ya) in the reduced image 6b is arithmetically obtained on the basis of data concerning four picture elements v0 to v3 which are closest to the above-described address (Xa'.multidot.Ya') in the original displayed image 6a. More specifically, first, pieces of data which respectively correspond to the picture elements v0 to v3 in the original displayed image 6a are read out from the arithmetic memory. Then, these pieces of read image data are respectively weighted in accordance with the distances from the address (Xa'.multidot.Ya') to the corresponding picture elements V0 to V3 and the weighted data values are averaged. Thus, it is possible to obtain a data value for any desired picture element va in the reduced image 6b.
On the other hand, when it is intended to prepare an enlarged image 7b enlarged, for example, Z times, on the basis of displayed image 7a as shown in FIG. 7a/7b, the address (Xb.multidot.Yb) of a picture element vb in the enlarged image 7b is reduced and projected on the original displayed image 7a to thereby obtain an address (Xb'.multidot.Yb') in the same way as in the case of FIG. 6a/6b. Then, pieces of data which respectively correspond to four picture elements v4 to v7 which are closest to the address (Xb'.multidot.Yb') are obtained. The pieces of read data are weighted in accordance with the corresponding distances and the weighted data values are then averaged. Thus, it is possible to obtain a data value for any picture element vb in the enlarged image of 7b.
The present inventor examined the above-described prior art and found that the prior art suffers from the following problems. Namely, static type RAMs and the like which are employed as arithmetic memories in image processing systems are means for reading data corresponding to one or more picture elements. That is, data stored in one or more memory cells, which are in fixed positional relation to a given picture element address. The prior art systems do not simultaneously read data stored in the memory cells which are closest to a designated address. Accordingly, it is necessary, in the case of effecting the above-described zooming of a displayed image, to execute the read operation of the arithmetic memory four times for each of the addresses of the picture elements in a reduced or enlarged image. This causes the time required for a zooming process to increase unnecessarily. It also increases the time during which the bit map processor is occupied, which results in lowering the processing capabilities of the system.